Some embodiments are directed to a new methodology aimed at preparing highly nitrogen-doped mesoporous carbon macroscopic composites, and their use as highly efficient heterogeneous metal-free catalysts in a number of industrially relevant catalytic transformations.
In this document, the numbers in italics and between brackets ( ) refer to the List of References given at the end of the document.
Re-thinking fundamental metal-based catalytic processes, in the light of tailored metal-free catalytic architectures, designed and fabricated from cheap and easily accessible building blocks, represent a challenging matter of the modern and really sustainable catalysis. Nitrogen-doped 1D and 2D carbon nanomaterials (N-CNMs) have emerged in the last decade as effective metal-free systems capable to promote efficiently a high number of catalytic processes (1-5). Recent studies have demonstrated how the inclusion of nitrogen(s) in the honeycomb carbon structure, breaks the electroneutrality of the Csp2 network (6, 7) and generates charged sites, with improved reagent's adsorption properties, capable to foster several catalytic transformations. Among the methods used for N-CNMs synthesis, the Chemical Vapor Deposition (CVD) still remains the most effective and widely used technique; other approaches like the annealing of CNMs in the presence of different nitrogen sources and the direct carbonization of N-containing organic precursors (3, 8) constitute valuable and alternative synthetic paths. At odds with the feasibility of these methods, nitrogen precursors with relatively high toxicity, i.e. dicyandiamide (9), melamine (10), polypyrrole (11), ammonia (12, 13, 14) along with generally high operation temperatures, under hydrocarbons and hydrogen atmosphere, are normally required to get the final N-doped materials. In addition, the low efficiency of these synthetic protocols generally results into a significant loss of the nitrogen and carbon precursors used, which calls for an extensive recycling of the exit gaseous reactants. Moreover, the harsh reaction conditions required to get N-CNMs are generally responsible for the generation of many waste by-products and for the growing process costs. Last but not least, many nitrogen precursors are relatively toxic compounds which often necessitate of specific precaution for their appropriate handling and processing. Alternative approaches to the N-decoration of CNMs, like the milder chemical functionalization of nanocarbon sidewalls and tips, have recently gain interest as an ideal paradigm for getting new insights on the role of N-functionalities as well as that of their chemical environment in specific catalytic transformations. In spite of their remarkable catalytic performance, these materials suffer of several limitations: from a high temperature sensitivity (that makes them ideal for low- or medium-temperature catalytic processes only) to severe synthetic restrictions (i.e. tricky upscale procedures and difficult material handling because of their powdery texture).
Therefore, there remains a need to overcome the main disadvantages known in the art and to devise a more straightforward and environmentally friendly synthetic methodology for the preparation of highly N-doped carbon-based materials. In particular, their achievement in the form of “highly flexible” coatings for a variety of macroscopic supports, thereby allowing access to a wide variety of composite materials for use as effective metal-free and environmentally friendly heterogeneous catalysts, still remain a challenging target for addressing a number of industrially relevant catalytic transformations.